Klein Ulrich, Alford Jacqueline A, Allshouse Amanda A, Sain Joel
Department of Pediatric Dentistry, Children's Hospital Colorado and School of Dental Medicine, University of Colorado Denver, Aurora, Colo., USA.
Private practice, Lawton, Okla., USA.
Pediatr Dent. 2016;38(3):198-202.
The purpose of this study was to determine, from a large number of panoramic images taken in the clinic of a pediatric dentistry residency program, the prevalence of maxillary nine-year molars (9YM), associated medical conditions (MCs), and the presence of coexisting tooth anomalies (TAs).
Pantomograms from 13,140 patients were searched for 9YM. Radiographs from identified subjects were examined for coexisting TAs, and charted MCs were noted. For identified 9YM, Nolla's stage of tooth formation was determined and the subjects' dental ages were calculated.
Among 53 subjects (68 percent females), 21 unilateral and 32 bilateral cases of 9YM occurred. Females and males were of similar age (7.98 versus 7.91 years old). Overall dental and chronological ages were significantly different: dental development in bilateral cases was delayed by 4.1 months in females and 2.9 months in both sexes (P=.003). In unilateral cases, it was accelerated by 3.6 months in females and 3.5 months in males. The specific tooth age for all 9YM was 4.95 years for females and 5.56 years for males (P=.018). The average count of associated findings (e.g., missing teeth, peg laterals, other TAs, and other eruption delays) was 0.62 in unilateral and 1.44 in bilateral cases (P=.02). Commonly associated MCs included clefting (N equals five), and Down syndrome (n equals three).
The prevalence of nine-year molars was one in 248 (0.4 percent), and the average delay in dental development was 2.7 years.
本研究旨在从儿科牙科住院医师培训项目诊所拍摄的大量全景图像中，确定上颌九岁磨牙（9YM）的患病率、相关医疗状况（MCs）以及共存牙齿异常（TAs）的情况。
在13140名患者的全景片中查找9YM。对已确定受试者的X光片检查是否存在共存的TAs，并记录所记录的MCs。对于已确定的9YM，确定诺拉牙齿形成阶段并计算受试者的牙龄。
在53名受试者（68%为女性）中，出现了21例单侧和32例双侧9YM病例。女性和男性年龄相近（分别为7.98岁和7.91岁）。总体牙龄和实际年龄存在显著差异：双侧病例中，女性牙齿发育延迟4.1个月，男女均延迟2.9个月（P = 0.003）。在单侧病例中，女性牙齿发育加速3.6个月，男性加速3.5个月。所有9YM的具体牙龄，女性为4.95岁，男性为5.56岁（P = 0.018）。单侧病例中相关发现（如牙齿缺失、钉状侧切牙、其他TAs和其他萌出延迟）的平均数量为0.62，双侧病例为1.44（P = 0.02）。常见的相关MCs包括腭裂（N = 5）和唐氏综合征（n = 3）。
九岁磨牙的患病率为248分之一（0.4%），牙齿发育的平均延迟为2.7年。
